The present invention relates to a method for the indirect determination of a specific formulation during an extrusion process in an extrusion device and an extrusion device for the production of an extrusion product.
It is known that extrusion products are produced with the help of extrusion devices. Thereby, for example films or blown films or cast films etc. are involved which are produced with an extrusion device. Herefore the extrusion device particularly provides a barrel extruder, in which a corresponding formulation is melted and conveyed. Thereby, an extrusion device can naturally also comprise more than one barrel extruder particularly a plurality of up to thirteen single barrel extruders. The requirements for extrusion products have increased in diverse manners, so that particularly multi-layered extrusion products should be equipped with for example different barrier properties for the film. Herefore diverse materials are necessary in order to configure the single layers of the extrusion product. With up to thirteen barrel extruders and each up to five materials therewith up to 65 different materials have to be fed in order to provide a single extrusion product with a multi-layered structure. Each specific extrusion product is thereby equipped with a specific material formulation. Such a specific formulation can thus comprise any amount of single materials between a single material and a plurality of up to for example 65 materials.
It is disadvantageously with known extrusion methods that the specific formulation can only be monitored with a high effort. Thus basically fully automated conveying systems are known which interact with silo systems. From a plurality of material silos each barrel extruder of the extrusion device is provided with a specific formulation according to the specific formulation. This is however an immense effort concerning the cost and the construction space for such a fully automated silo plant. Normally, the single materials are filled in barrel-like into the storage tanks and starting from there are supplied to the extrusion device for example using suction lances. Likewise, by the suction lances storage tanks can be filled in form of weight funnels or storage funnels. In all cases a manual adjustment of the formulation occurs in form of conscious stretching of the suction lances or explicit filling of materials in the respective storage tanks. All of this occurs manually by the operator of the extrusion device. Accordingly human sources of error are given by such a manual handling, so that the risk of an incorrect material composition for the specific formulation exists. An incorrect material composition can lead to an incorrect extrusion product for example in form of an incorrect composed multi-layered film. This leads again to film properties or product properties of the extrusion product which differ more or less intensely from the desired product. Such product properties can for example involve the sealability, the transparency, the weight or the barrier properties of this extrusion product. In a worst case an incorrect formulation is only apparent after completion of the whole extrusion product, when it shall be used in the further processing with the costumer. In such a case the whole extrusion product has to be regarded as waste which involves a high material and cost damage.
A further disadvantage is that even the clearly marked and with a detailed data sheet specified raw materials are dependent on more or less intense batch variations. This can on the one hand be the direct result of the polymerisation process with which batch variations occur in more or less narrow tolerated limits. On the other hand it is common today that due to the increasing globalisation the same raw material is produced at different production sites and the batch variations can be pronounced partly significantly stronger. Batch variations of single raw materials can have a negative influence on the process control and also on the resulting properties. Quality defects and complaints resulting from batch variations are hard to prove towards the raw material supplier from the processor's point of view and the resulting quality costs are often borne by the processor.
Many producers of plastic films control the delivered raw material on a regular basis also related to batch variations within the scope of the incoming goods inspection. Thereby, the often mentioned MFI (melt flow index) is determined, which is a “one point method” for the determination of the viscosity properties of a plastic. This method however has multiple disadvantages:                a complex laboratory test, particularly when many plastics have to be measured multiple times,        a reproducibility and comparability of the measurement results is partly only possible on a limited basis, since the measurements underlie multiple disturbances,        the viscosity of plastics is a complex scale dependent from temperature and shear rate and this is only described incompletely by the MFI “one point” measurement.        